The main techniques and approaches of biochemical cytology, resting largely on the combined use of cell fractionation, enzymology, biochemistry, and electron microscopy, are applied to a detailed analysis of the subcellular events underlying the pathogeny of atherosclerosis. The experiments will be carried out on human arteries, obtained at autopsy or surgery, and on arteries of rabbits fed on a cholesterol diet. The studies will focus on all major organelles, with particular emphasis on lysosomes and peroxisomes which previous work has shown to be markedly altered in atheromatous arteries. Special attention will be paid to the nature of lipids accumulating in lysosomes or stored as lipid droplets in arterial cells.